Before Hurricane Sandy, Geoff Manaugh wondered what the New York City region would look like if massive flood barriers—similar to what some people have proposed in the past few days—lowered the Hudson and East Rivers and excavation exposed riverbeds’ slopes:
In 2057, massive flood-control structures protecting New York City from the rising seas required a redirecting of the Hudson and East Rivers northeast, into Long Island Sound. The resulting dams—the construction of which triggered small earthquakes throughout New England—allowed for the draining of the old riverbed south and east of Manhattan, revealing the unearthly geological circumstances on which this archipelagic metropolis sits.
Sounds similar to Atlantropa, but smaller and less audacious.